The new fire also threatened the hilltop campus of one of the world's richest museums, even as more than 1000 firefighters in nearby Ventura County battled the biggest of the wind-fed blazes, which threatened more than 12,000 homes.

A brush fire erupted overnight and quickly spread, creating an alarming spectacle for pre-dawn commuters on the hillsides east of Interstate 405 before the California Highway Patrol closed the heavily travelled freeway.

The Skirball Fire, the newest of several uncontained brush fires that have sprung up in Southern California since Monday, prompted officials to order residents of the hilly, wooded area west of the Bel Air neighbourhood out of their homes.

Among the properties at risk is the house and winery of media mogul Rupert Murdoch.

It was not immediately clear how many people were affected by the evacuation order in the area south of scenic Mulholland Drive and north of Sunset Boulevard.

The nearby Getty Center museum said it shut down for the day to protect its art collection from smoke damage.

The largest of the fires, known as the Thomas Fire, raged in and around the city of Ventura, 80km northwest of Los Angeles, fire officials said. The blaze has charred more than 26,000ha in Ventura and its foothills, they said.

The entirely uncontained blaze was whipped by intensifying, dry Santa Ana winds blowing westward from the California desert. Gusts were forecast to top out at 115km/h on Wednesday and remain strong through the week.

California Governor Jerry Brown declared a state of emergency on Tuesday, freeing state funds and resources to assist firefighters. The Federal Emergency Management Agency said it approved grants to help cover the cost of emergency work for the Thomas Fire and two others.

Although no casualties have been reported, the fires have destroyed at least 150 homes, forced mass evacuations, cancellation of classes of dozens of schools and resulted in the loss of power at more than 250,000 homes in Ventura County.